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DA100 (50Hz) and DA50W Chassis – Repair Notes 

 

To ensure good linearity of the mains supply voltage waveform, it is necessary to ensure that current is taken at 
the start of the voltage cycle, i.e. zero voltage switching.  This function is achieved with the use of a Power 
Factor Correction Circuit.  It is located between the main bridge rectifier and main reservoir capacitor and is 
physically located on a sub-board on the left-hand side of the main chassis (when viewed from the rear of the 
set.  The board will also have the focus modulator circuit on it (76cm and some 66cm models only).  
The circuit is basically a DC to DC converter that increases the power supply input voltage to about 400VDC.  
Note that the main reservoir capacitor, C705, is decreased in value and increased in voltage rating because of 
this.  It is a 68µF rated at 450V in power factor module sets, and a 220µF, 385V capacitor in non-power factor 
module sets. 

Sharp Electronics (UK) Limited - May 2003 

 

DA100 (50Hz) and DA50W Chassis – Repair Notes 

 

 
Note that on the 56FW53H the Power Factor PWB is mounted at the front of the set, underneath the CRT. 

 
 
 

 

Sharp Electronics (UK) Limited - May 2003 

 

DA100 (50Hz) and DA50W Chassis – Repair Notes 

 

In some cases the HT can rise to over 200V, this can cause damage to other parts of the circuitry.  This is 
normally caused by failure of IC705 - the power supply voltage regulation feedback opto coupler.  The device is 
easily damaged by excessive heat while soldering, so remember to keep your soldering iron turned down to 250

o

C 

or below, and not to solder for more than 10 seconds on  each  leg.    If  these  conditions are not met the 
transparent barrier between the LED and opto transistor will be damaged.  Note that sometimes the set will 
work for several weeks or months before failing if the opto has been damaged during fitting.   
To alleviate damage to other parts of the circuitry when the HT rises, an avalanche diode was fitted across the 
main HT smoothing capacitor (C720) from late 1999 production.  This device has a rated maximum voltage of 
170V, and will go short circuit if this voltage is reached.  If the avalanche diode was not fitted, it is worthwhile 
to check the following components for damage before turning the set on.  Note that this diode must be fitted to 
all chassis (part number RH-EX0875BMZZ). 
 

Q601 

Horizontal output transistor 

RH-TX0192BMZZ 

Leaky or short circuit 

IC301/2 

Audio output IC’s 

VHITDA7480/-1 

Short circuit.  Also check supply feed chokes 

IC1801 

CDA IC on CRT base PWB 

See previous list 

Short circuit.  Check pin 5 to ground (<500Ω) 

C720 

HT reservoir capacitor 

RC-EZ0258CEZZ 

Physically damaged 

IC1301 

Centre channel amplifier 

VHITDA7480/-1 

Short circuit.  Located on centre speaker PWB 

Q5407 

Scan velocity modulator transistor 

VS2SA1837//-1 

CRT PWB – short or open circuit 

Q5408 

Scan velocity modulator transistor 

VS2SC4793//-1 

CRT PWB – short or open circuit 

L315/6 

IC302 feed chokes 

VP-CF3R3K0000 

Open circuit 

L350/1 

IC301 feed chokes 

VP-CF3R3K0000 

Open circuit 

Sharp Electronics (UK) Limited - May 2003 

 

 
 

DA100 (50Hz) and DA50W Chassis – Repair Notes 

 

 
 

 
 
 
 
 
 
 
 

 
 

 
 
 
 
 
 
 
 
 
When the avalanche diode is fitted, only four components generally need to be replaced (D735, Q601, IC705 and 
C720), this is because it prevents further damage to the circuitry should the power supply be kept running.  
Sharp produce a kit that contains these four items - use the part number FWSERVKIT01// 
 
If the set is operated for prolonged periods without the avalanche diode fitted, then damage will occur to other 
parts of the circuit.  The CRT PWB suffers normally all the electrolytic capacitors have to be replaced if this is 
the case.  The moral is, DO NOT run the set when high HT is present. 

Sharp Electronics (UK) Limited - May 2003